An image sensor is formed of sensing elements which are referred to as picture elements or "pixels". The resolution of an image sensor is a direct function of how many pixels there are in a matrix of rows and columns. A sensor having, for example, 500 horizontal pixels per row will have a lower resolution than one which has 1,000 horizontal pixels per row.
In the present invention the output images from a system incorporating a monochrome sensor and a color filter wheel are increased in resolution without an increase in the resolution of the image sensor. The present invention sequentially scans an image such as a film image and combines the signals resulting from the scanning to increase the resolution of an output image.
U.S. Pat. No. 4,638,371, "Multiple Exposure of Area Image Sensor Having a Sparse Array of Elements" by James R. Milch, assigned to Eastman Kodak Company, the assignee of the present invention, teaches a method for obtaining a high resolution image sensor by combining multiple scanned images which are optically offset by angled glass plates. Precisely controlled servo motors are needed to properly position the glass plates.
A single image sensor can be used to provide red, green and blue color separation images from a film image by sequentially placing a series of color filters between the film and sensor. A patent which teaches this technique is U.S. Pat. No. 2,435,962 entitled "Color Television" by P.C. Goldmark et al wherein a rotatable color wheel having repeating transparent red, green and blue segments is provided. Additionally, segments of two different thicknesses are used. A light beam intersects one segment at a time as the wheel is rotated and is displaced by a distance that is a function of the thickness of the segment, which is set to provide a vertical offset corresponding to one scan line. This method does not increase the resolution of the output image, but instead eliminates color crosstalk when used in an interlaced field sequential color television system.
Another patent of interest for its teachings in this area is U.S. Pat. No. 4,786,964 entitled "Electronic Color Imaging Apparatus with Prismatic Color Filter Periodically Interposed in Front of an Array of Primary Color Filters" by W. T. Plummer et al. The apparatus of that patent uses a color wheel having four openings. Within two opposing openings a prismatic magenta filter is positioned to remove the green component of the image and to shift the remaining components of the image by a fixed amount. A subtractive tricolor filter is positioned between an array of CCD light detecting elements to receive the shifted and non shifted image components.
The electrical signals representing the shifted and the non shifted images may be stored and later recombined by counter shifting the shifted image from the magenta filter and combining the two images. The aforementioned apparatus solves the problem of a dominant green color component being detected by the CCD array which arises because the subtractive tricolor filter allows the green component of an image to be received by all of the CCD sensing elements whereas the red and blue components will each be received by only one third of the total number of CCD sensing elements. Shifting the image with the magenta filter removes the green dominance problem, but does not increase the resolution of the image beyond the resolution of the sensor.